It is desirable to provide a plastic closure with a press-on screw-off structure that is adapted for high speed production, for easy use on containers, and well adapted for vacuum capping operations. It is also desirable to provide a plastic closure having sealing and retention functions that can be optimized by selection of proper thermoplastic materials for such sealing and retention functions.
In the past, for example, in U.S. Pat. No. 3,371,813 (Owen et al) there is proposed a closure with a soft, readily deformable gasket material inside the pheripheral skirt of a metal closure, the gasket material being said to deform readily and flow around the threads of a container to form cooperating thread grooves in the gasket material. This formation of well defined, cooperating set grooves in the gasket for contact with the ribs, the grooves providing leverage on the threads to permit opening of the container by twisting the metal cap. The gasket material is said to be cast in situ on the skirt and in the side of the top of the closure to form a liner. The patent also suggests that the resilient deformable gasket material have ribs that are at least 20% and generally 30% to 70% of the total circumferential surface area of the gasket skirt to provide increased package security and greater cam off force against the continuous or discontinuous threads of the container.
U.S. Pat. No. 4,000,825 (Westfall) describes a press-on twist-off metal closure of the type described in the above Owen et al patent for oxygen sensitive products. The patent describes a top liner having spaced-apart vertical ribs inside the skirt of the shell of the closure. The liner is formed preferably from a foamed plastisol material that deforms and cold flows around the threads of the neck of a container to form a series of thread-cooperating cavities in the foamed liner to aid in removal of the closure using a twist-off motion. In addition, the patent shows a top seal as well as the sealing obtained by deformation of the gasket material around the threads.
In U.S. Pat. No. 3,270,904 (Foster et al) there is a press-on turn-off metal cap, the cap having a gasket material at the top and around the bottom of the skirt, the gasket material in the skirt engaging the threads of the container. The gasket material is described as a plastomeric and takes a conformation to form a hermetic seal cooperating with the thread means of the container finish. The plastomeric material hardens to form rigid thread grooves therein for the camming operation with the raised threads of the neck of the container.
U.S. Pat. No. 3,606,062 (Frisch et al) discloses a crimpon twist-off metal crown cap with top and corner seals. There are deformable metal flutes in the metal shell to engage the threads of the container.
U.S. Pat. No. 3,448,881 (Zipper) discloses a metal closure with a gasket for engaging the threads of a container, the metal closure having means to prevent increase in cap removal torque including a ridge on the underside of the cap to prevent settling of the cap due to gradual deformation of the gasket material. Grooves are formed in the gasket by the threads of the container when the metal cap is applied to the threads. In FIG. 5 of the Zipper patent, a series of dimples 41 are provided in the top wall of the cap. However there is no suggestion of interengaging parts that dovetail together for a strong locking force in the skirt area of the cap.
In general, in the above patents that describe metal caps with soft deformable gaskets, there is substantial contact between the deformable gasket ribs and the container threads such as contact of the entire rib or as, for instance, in the Owen et al patent, the ribs are shaped for substantial contact with the threads and comprise 20% up to 70% of the gasket area.
It is an object of the present invention to provide an all-plastic closure for a container, the closure comprising a hard plastic shell with a top and a skirt and a deformable plastic gasket material as a liner inside the top and as a gasket material located on the inside skirt of the shell, the gasket and the shell being so constructed and arranged that when the gasket is formed inside the shell, there is no rotation of the gasket with respect to the shell.
It is an object of the present invention to provide a closure for a container, the container comprising a neck finish area with generally helical threads, the closure comprising a thermoplastic cap having a top and a peripheral skirt, a gasket member of resilient plastic located next to the shell of the cap, the gasket member including a skirt located just inside and concentric with the shell of the skirt, there being a plurality of ribs in the gasket material on the inside thereof for deformation around the threads of the container when the cap is closed over the threads, the area of all the ribs being less than about 10% of the circumferential surface area of the gasket skirt, there being sufficient ribs to adequately retain the cap when subject to normal abuses in shipping and handling, the gasket material and cap shell being held together by spline means including spaced-apart vertical splines and corresponding cooperating grooves in the cap skirt and in the gasket member that are like gear teeth so that the gasket member and shell will not rotate with respect to each other.
It is an object of the present invention to provide a thermoplastic closure for a container having threads in the neck area, in which there is a deformable portion in the skirt of the cap that will deform to the contour of at least a portion of the threads when the closure is pressed on and in which there is spline means for dovetailing the deformable portion and the shell skirt together so that the deformable portion does not rotate with respect to the shell.
It is an object of the present invention to provide a thermoplastic closure comprising a plastic shell and an inner deformable gasket to engage a container having threads, the closure being easy to manufacture, easy to decorate, easy to use and the shell and gasket being held together by dovetail means to prevent rotation, the resulting closure being accommodating of finish irregularities and being capable of seal and retention function optimization.